Living on the edge in the North Pacific....with two kids, two dogs, a manic husband and a wife who tries to keep up with the pack.

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Tuesday, August 06, 2013

GPR at the Kashevaroff Site

John S and Ryan C and the ground penetrating radar set up

Last week Ryan and John visited the site with ground penetrating radar and looked for sub surface features. Ryan is a geologist who does remote sensing work for a company called TerraSond. He is married to Molly Odell (the Community Archaeology PI for the last couple of years) and has visited our excavations in the past. His visits piqued his interest in how well his remote sensing equipment would work at picking up underground archaeological features. Could ground penetrating radar find buried features and help us archaeologists decide where to dig?

So last week he dropped in with his ground penetrating radar gear to give it a try. Northwest Geophysics kindly loaned Ryan the gear free of charge. I showed Ryan the site and pointed out that we had only excavated half of a late prehistoric house. Outside of our excavation the rest of the depression and a possible small side room are clearly visible. It was a perfect opportunity to see how the GPR worked.

So Ryan and John dragged the sled across the ground in a 6 by 6 meter grid and imaged what was below the surface. It matched up pretty well with what we expected to find - and even shows a potential rock pile associated with the side room. Side rooms often have rock piles of firecracked rock that represent the remains of saunas. Water was thrown on hot rocks to create steam. However, the GPR did not see much in the underlying deposits. We also had him scan the surface of our excavation - and he really did not see anything.

Ryan and John then went exploring about the site and found another slight depression 60 meters or so to the southwest of our excavation. We determined that it is cultural when a soil probe turned up charcoal. Now to see what the GPR could see. And it did pretty well. It looks like another late prehistoric house depression! Next year we hope to excavate this feature and see exactly how well the GPR did at outlining the depression.

I was pretty happy with how well the GPR mapped out the late prehistoric houses. But a little disappointed with its abilities to find older features (and it turns out it missed one in the southeast corner of our excavation). I still think that good old fashioned test pits and soil probes are the best way to find archaeological sites, and the limits of sites. But the GPR does 'see' rock piles and house depressions pretty well and I can see using one in the future to help position excavation blocks.

I am very happy with Ryan, TerraSond, and Northwest Geophysics for giving us the opportunity to use ground penetrating radar. Thank YOU!

Patrick

A figure from Ryan's report that shows how the GPR did with the unexcavated sideroom

GRP results of the new house depression that John and Ryan found (seen in top photo)